Actuating means for telemechanic fluid power steering system



Dec. 26, 1961 v P 'DQNNER ETAL 3,014,548

ACTUATING MEANS FOR TELEMECHANIC FLUID POWER STEERING SYSTEM Filed Nov. 13, 1959 3 Sheets-Sheet 1 A TTOR/VEY Dec. 26, 1961 v. P. DONNER ET AL 3,014,548

ACTUATING MEANS FOR TELEMECHANIC FLUID POWER STEERING SYSTEM Filed Nov. l5, 1959 5 Sheets-Sheet 2 Dec- 26 1961 v. P. DONNER ET AL 3,014,548

ACTUATING MEANS FOR TELEMECHANIC FLUID POWER STEERING SYSTEM Filed Nov. 13, 1959 `3 Sheets-Sheet 3 A 7' TUR/VE Y United States Patent Utilice 3,014,548 Patented Dec. 26, 1961 3,014,548 ACTUATING MEANS FOR TELEMECHANIC FLUID POWER STEERING SYSTEM Verne I. Donner, Palatine, and William W. Henning,

Hinsdale, Ill., and George S. Allin, Jr., Burlington,

Iowa, assignors to International Harvester Company,

Chicago, Ill., a corporation of New Jersey Filed Nov. 13, 1959, Ser. No. 852,639 3 Claims. (Cl. 180-79.2)

This invention relates to a fluid power steering system of the follow-up type. More in particular this invention relates to an hydraulic power steering system for a twowheel tractor pivotally connected to a trailer vehicle such as a road scraper.

Power steering mechanisms generally are provided with an independent source of iluid under pressure usually in the form of a low capacity iluid pump driven by the vehicle power plant. Under certain conditions particularly at low engine speeds, rapid angular displacement of the tractor with respect to its trailer is impossible because of insufficiency of fluid delivery under pressure from the pump.

Most tractors of the two-wheel Itype are provided with a relatively large capacity uid pump to serve utility purposes such as hydraulic rams for dumping a loaded trailer or controlling the ground engaging elements of a scraper. In our co-pending application, Serial No. 653,- 802 tiled on April 19, 1957, now Patent No. 2,917,125, this application being a continuation-in-part thereof, there is described a uid power steering system of the followup type employing one source of iluid under pressure for ordinary steering but is adapted to employ also a second source of uid under pressure, such as the tractors utility pump, for extraordinary steering requirements. Although the present invention about to be described is applicable to singular and multi-sources of fluid under pressure steering systems, the hydraulic arrangement described in the aforesaid co-pending application will be employed to illustrate an embodiment thereof.

The prime object of the present invention is to provide means for actuating the follow-up or telemeter mechanism in fluid power steering mechanisms.

-Another object of the invention is to provide diiferential fluid pressure means for actuating the follow-up or telemeter mechanism in fluid power steering mechanisms.

A further object of the invention is to provide a cam operated servo-pump device for actuating the followup mechanism in a iluid power steering system.

A still further object of this invention is to provide a cam operated servo-pump device for telemechanically actuating a uid controlled hydraulic power steering mechanism.

These and other important objects inherent and encompassed by the invention will be more readily understood from the ensuing description, the appended claims and the annexed drawings wherein:

FIGURE l is a side elevation of a two-wheeled tractor and associated trailer illustrating a general environment on which this invention may be utilized.

FIGURE 2 is a plan view, partly broken away, taken on line 2-2 of FIGURE 1, illustrating the general arrangement of a preferred form of the angular displacing elements for steering a two-wheeled tractor and trailer according to this invention.

FIGURE 3 is a side elevation, partly in section and partly broken away, taken on line 3--3 of FIGURE 2, showing a detailed construction of the pivotal hitching mechanism of the tractor to the trailer including the power unit for effecting angular displacement of the tractor with respect to the trailer.

FIGURE 4 is a side elevation in section taken through the longitudinal medial line of the uid control valve.

FIGURE 5 is a schematic drawing illustrating the entire hydraulic system including the preferred form of cam operated means of the invention for actuating the follow-up mechanism.

FIGURE 6 is a similar to a portion of FIGURE 2 except that a modified form of cam operated means, according to this invention, is shown for actuating the followup mechanism.

FIGURE 7 is similar to a portion of FIGURE 5 showing the hydraulic connections, schematically, for the modified form of the invention illustrated in FIGURE 6.

Referring now to the drawings illustrating a preferred embodiment of the invention, it will be seen from -FIG- URE 1 that the numeral 10 generally indicates a twowheeled tractor having a power plant or engine 11 supported by a pair of ground engaging traction wheels, one of which is shown at 12. The numeral 13 generally indicates a trailer, such as a road scraper, supported on the rearward portion by a pair of ground engaging wheels, one of which is shown at 14. The forward portion of the trailer 13 is pivotally connected to the rearward portion of the tractor 10 in a well known manner as generally indicated at 15.

Referring now to FIGURES 2 and 3, the portion of the pivotal connection 1S mounted on the rearward portion of the tractor 10 may comprise a housing or casing 16 pivotally mounted on a longitudinal shaft 17. The shaft 17 is journalled to the tractor frame 18 on the two axially alined bearing assemblies generally indicated at 19 and 20. From this it can be seen that the casing 16 may rotate to a limited degree longitudinally with respect to the tractor 10 for purposes later explained. The casing 16 also includes an upwardly extending yoke 21 which supports the upper end portion of a king pin 22. The lower portion of the king pin 22 is supported by the casing as is generally indicated at 23 as best shown in FIG- URE 3.

A carrier member 24 is pivotally mounted on the king pin 22 and connected rigidly to a large pinion gear 2S by a plurality of bolts, two of which are shown at 26 and 27. A connecting element 28 (FIGURE l) commonly referred to as a goose-neck of the forward portion of the trailer 13 is rigidly connected to the carrier member 24 by any suitable means such as bolts (not shown). Thus the trailer 13 may pivot about the king pin 22 in substantially a vertical plane and forms a hitch between the trailer 13 and tractor 10. The shaft 17 permits limited longitudinal movement of the casing 16 and trailer 13 with respect to the tractor 10 so that deviations in ground conditions do not impose unnecessary lateral strain on the king pin 22 and its supporting elements.

The rearward portion of the casing 16 is provided with a uid powered reversible motor generally indicated at 29. The reversible motor 29 may conveniently be cornprised of a rst single-acting ram 30 and a second singleacting ram 31 disposed in opposed parallel relation with respect to each other. The ram 30 is provided with a piston 32 and connecting rod 33. The rod 33 may be integrally or pivotally connected to a firstrack mem-ber 34 having inwardly extending gear teeth 35 in engaging relation with the pinion gear 2S as best shown in FIGURE 2. Thus it may be seen that fluid under pressure entering the chamber 36 through the port 37 urges the piston 32 forwardly for moving the pinion gear in a counter-clockwise direction as viewed in FIGURE 2. It should be noted that a roller 38 is mounted on the casing 16 for vertical axis rotation and in engaging relation with the outer edge 39 of the rack member 34 so that the member 34 is maintained in meshed relation with the pinion gear 25 as best shown in FIGURE 2.

Similarly the ram 31 is provided with a piston 40 and connecting rod 41. The rod 41 may be integrally or pivotally connected to a second rack member 42 having inwardly extending gear teeth 43 in engaging relation with the pinion gear 25 as best shownin FIGURE 2. Again it may be seen that fluid entering the chamber 44 through the port 45 urges the piston 40 forwardly for moving the pinion 25 in a clockwise direction as-viewed in FIGURE 2. It should again be noted that aroller 46 is mounted on the casing 16 for vertical axis rotation and in engaging relation with the outer edge 47 of the-rack member 42 so that the member 42 is maintained in meshed relation with the pinion gear 25 as best shown in FIGURE 2.

Now it can be appreciated that when one of the rams 30 and 31 expands, the other correspondingly retracts. In order to prevent damage to a retracting ram due to the engagement of the rearward face of its piston with the rearward end portion of the casing 16, the ports 37 and 45 each are provided with a snubbing valve, one of which is indicated at 48 in FIGURE 3. The snubbing valves serve to terminate the exhausting of fluid through the ports 37 and 45 when either of Athe pistons 32 or 40 is retracted to a predetermined limit. Although not a part of the present invention, the snubbing valves may conveniently be comprised of a captive spring 49 positioned to urge forwardly a valve stem 50 to its limit formed by an enlarged portion 51 abutting a corresponding shoulder 52 Vformed in the casing 16. Retracting of the piston 32 causes the rearward side thereof to engage the valve stem 5,0 fr further compression of the spring 49. Movementl of the valve stem 50 rearwardly progressively closes or throttles the port'37 so that rearward movement of thev piston 32 is dampened initially and ultimately stopped 'by confined iluid in the chamber 36Y before abutting therear end4 wall of the casing 16. Thesnubbin-g valve disposed at the port 45 is similar in construction to the snubbing valve at the port 37 vabove described.

For purposes later to be described the powerv steering mechanism, according to this invention, isprovided withi a servo-pump; The servo-pump may conveniently be comprised of a left cylinder generally indicated at 53 `and a right cylinder generally indicated at 54. IEach of the cylinders 53 and 54 is constructed similar to relatively small single-acting hydraulic rams having their respective housings mounted rigidly on the casing 16. The cylinders 53 and 54 are positioned in opposed relation with respect to the pinion gear 25 as best shown in FIGURE 2.

The left cylinder 53 of the servo-pump is provided with a reciprocable piston 55 connected to an externally protruding actuating pin 56. Ou the outer edge of the rack member 42 there is disposed a cam 57 in the form of a longitudinal tapering groove, the taper being in an inward direction from right to left on the-rack 42 as viewed in FIGURES 2 and 5. The inward sideof the groove form-V ing the cam 57 is thus-essentially linear incharacter and forms a cam surface 58 in alinement with the actuating pin 56 so that the outer end of the pin 56 slidably abuts the cam surface 58 as a. cam follower. From this it can be seen that as the rack member 42 is moved by the expansion of the ram 31 the actuatingpin 56 in engagement with the cam surface 58 moves the piston 55' of the cylin der 53 in a retractive direction thereby causing movement ofuid in the chamber 59'and its connecting port 60. Although not of critical necessity as will be later understood, a compression spring 166 may be inserted in the cylinder 53 in abuttingrelation with the outer side ofthe piston 55 for urging the piston 55 and its associated actuating pin 56 inan inward direction for maintaining-constant engagement of the pin 56 with thecam surface 58 when the ram 31 is moved retractively.

Similarly the right cylinder 540i the servo-pump isprovided with a reciprocable piston 61 connected to an externally-protruding actuating pin 62 asshown in FIGURE I 2. 0n the outer edge of the rack member 34 there is disposed a cam 57' in the form of a longitudinal tapering groove, the taper bein-g in an inward direction from right to left on the rack 34 as viewed in FIGURES 2 and 5. The inward side of the groove forming the cam 57 is thus linear in character and forms a cam surface 5-8 in alinement with the actuating pin 62 as a cam follower. Thus it can be seen that as the rack member 34 is moved by the expansion of the ram 30 the actuating pin 62 in engagement with the cam surface 5S moves the piston 61 of the cylinder 54 in a retractive direction thereby causing movement of fluid in the chamber l63 and its connecting port 64. As before, a compression spring 167 may be, but not of critical necessity, inserted in the chamber 63 of the cylinder 54 in abutting relation with the outer side of the piston 61 for urging the piston 61 and its associated ac tuating pin 62 in an inward direction for maintaining constant engagement with the cam surface 5S when the ram 30 is moved retractively.

From the foregoing it can be appreciated that when the pinion gear 25 associated with the trailer 13 is rotated with respect to the casing 16 associated with the tractor 1d, fluid is exhausted from the servo-pump through one of the ports 60 and 64 and tluid is entering the servopump through the other of the two ports 65) and 64. It will be observed that in the camming means for actuating the servo-pump 53, 54 the cams 57 and 57 are advantageously integral with the rack members 34 and 42 which permits some latitude in positioning the cylinders. 53 and 54 with respect to the king pin 22 and the actuating pins 56 and 62 ,can be of relatively short length as is evident vfrom FIGURE'Z. Furthermore, this form of camming means does not involve space requirements in or about the congested space of the hitch means around the king p in 22.

Reference is now made to FIGURES 6 and 7 of the drawings illustrating a modified form of the invention for cam actuating the servo-motor. Although the modied form of the invention is illustrated and described in our copending application, now Patent No. 2,917,125, it is appropriate to describe it here briefly.

Each of the cylinders 53 and 54 of the servo-pump may be positioned on the casing 16 either as shown in FIGURE 6 or FIGURE 7. It will be noted that in either case the longitudinal axes of the cylinders 53 and 54 are alined to intersect the axis of the king pin 22 and that the cylinders 53 and 54 are also in opposed relation to each other.

On the upper portion of the pinion gear 25 thereis disposed a cam 57" constrained for rotation with the pinion gear 25. The cam surface 58" of the cam 57" is in alinement with and in abutting relation with the actuating pin 56' of cylinder 53 and the actuating pin 62 of the cylinder` 54. It will be noted that the actuating pins 5 6. and 62 shown in FIGURE 6 are considerably longer than the actuating pins 56 and 62 of the irst form of the invention shown in FIGURE 2. The cam 57 may conveniently be circular in shape but positioned in eccentric relation with respect to the pinion gear 25 as best shown in FIGURE 6.

From the above it can be appreciated that when the pinion gear 25 and cam 57" associated with the trailer 13 is rotated with respect to the casing 16 associated with the tractor, fluid is exhausted through one of the portsA 60 and 64 and uid is ventering through the other of the two ports 60 and 64.

The general construction of the hitch connection between the trailer 13 and the tractor 10 and the powerunit of the steering mechanism has now been described. At this point it is suicient to say that inorder to steer the tractor 10 and its associated trailer 13, it is necessary to create forcibly and controllably an angular displacement between the longitudinal axis of the tractor 10 with respect to the longitudinal axis of the trailer 13. Such angular displacement can be accomplished by energizing controllably one of the rains 3 or 3-1 appropriate to the direction desired.

One of the components employed to control the energizing of the rams 30 and 31 appropriately is a control valve 65 illustrated in FIGURE 4. For purposes of this invention it is immaterial Whether the control valve 65 is adapted for operation with one or two sources of fluid under pressure as will be evident herein. Since the preferred embodiment employs an hydraulic system having two sources of uid under pressure, an appropriate valve control 65 therefor will be described and its operation is exactly as that described in our aforesaid co-pending application now Patent No. 2,917,125.

The control valve 65 may be comprised of a housing 66 including an end-wall 67 on one end thereof and a closure member 68 on the other end thereof. The casing 66 is provided with a longitudinally disposed bore 69. The housing 66 is provided with a first annular groove 70, a second annular -groove 71, a third annular groove 72, a fourth annular groove 73, a dfth annular groove 74 and a sixth annular groove 75 in parallel arrangement concentric with the bore 69 as best shown in FIG- URE 4. The annular grooves 70 through 75 form lands 76, 77, 7S, 79 and 80 in the bore 69.

Disposed in slidable relation in the bore 69 is a movable valve member or plunger generally indicated at 81. The valve member 81 is provided with a first circumferential groove 82, a second circumferential groove 83, a third circumferential groove 84 and a fourth circumferential groove 85 in parallel relation. The circumferential grooves 82 through 85 form lands 86, 87, 88 and 89 as illustrated in FIGURE 4. The annular groove 70 isconimunicatively connected to a discharge port 90. Also, the annular groove 74 is communicatively connected to the discharge port 90 through the port 91 and the laterally extending conduit 92 shown in FIGURE 5. The annular groove 71 is provided with a first fluid outlet port 93 connected to the conduit 94 which conduit 94 is communicatively connected with the port 37 of the first ram 30. The annular groove 73 is provided with a second fluid outlet port 95 connected to the conduit 96 which conduit 96 is communicatively connected with the port 45 of the second ram 31.

In the control valve 65 there is disposed a check valve generally indicated at 97 having its inlet side 99 in communication with the discharge port 90 and its outlet side i! in communication with the conduit 165. The conduit 165 is communicatively connected to the internal portion of the casing 16 which may conveniently serve as a sump or reservoir 162 of the fluid return means. The check valve 97 is urged into closed position by a captive spring 162 selected so that fluid in the discharge port 90 is maintained at a predetermined low value, for example 25 p.s.i. Thus when the luid pressure in the discharge port 90 exceeds the predetermined value, the check valve 97 opens to allow excess uid to escape through the conduit 165 back to the sump or iluid reservoir 162.

Disposed in the upper portion of the control valve 65 is a primary inlet port 103 and a secondary inlet port 104'. The port 103 is communicatively connected to a primary source of uid under pressure such as a pump 105, shown schematically in FIGURE 5, by the conduit 4106. A unidirectional flow valve, generally indicated at 107 (FIGURE 5), may be interposed in the conduit 106 to prevent reverse ow of uid to the pump 105 should the pump 105 fail or uid pressure in the conduit exceed the pressure delivered by the pump 105. The secondary inlet port 104 is communicatively connected to a secondary source of fluid under pressure such as pump 108, also shown schematically in FIGURE 5, by the conduit 109. It should be mentioned that the primary source of uid under pressure 105 is of relatively small capacity but suicient for steering under normal conditions. On the other hand, the secondary source of fluid under pressure 108 is of relatively large capacity and is basically intended for utility purposes such as operating lifting elements and the like. However, both sources of fluid under pressure are employed combinedly under certain steering conditions when the primary source is insui-cient to meet emergency requirements and will be further discussed in the description of the operation of the steering mechanism.

Communicatively connecting the third annular'groove 72 with the primary inlet port 103 of the control valve 65 is `an elongated compartment 110. A bore 111 is disposed longitudinally -in the housing 66 which intercepts the compartment 110. A bore 112 in axial alinement with and smaller than the bore 111 is disposed in the casing 66. The bore 112 is communicatively connected with the iifth annular groove 74 through the passage 113 shown in dotted lines in FIGURES 4 and 5. Within the -bore 111 is a relief valve generally indicated at 114 having a slidable element 115 which seats on the shoulder 116 of the casing 66. A captive spring 117 urges the element 115 into seating engagement With the shoulder 116. From this it can be seen that since the bore 111 is of larger diameter than the bore 112 a nid pressure in the compartment exceeding a predetermined maximum value will move the slidable element leftwardly to further compress the spring 117 and consequently disengage the element 115 from seating relation with the shoulder 116 thereby permitting the excess uid to escape into the bore 112, passage 113 to the annular groove 74 which groove communicates with the discharge port 90 through the conduit 92 as previously explained. Now in order to prevent a chattering movement of the slidable element 115 of the :relief valve 114, a small pass-age 118 is formed in the element 115 which communicatively connects the bore 112 with the spring chamber 119. Thus, movement of the element 115 is dampened because uid in the spring chamber 119 and the bore 112 must pass through the small passage 118 as a resulting consequence of any longitudinal movement of the element 115. From this it can readily be seen that by selecting appropriately the size of the passage 118 the movement of the element 115 can be dampened as required.

The control valve is also provided with a second relief or check valve generally indicated at 120. In order to accommodate the relief valve 120, there is provided a bore 121 in the casing 66 which bore extends to the compartment 110. The valve is comprised of a slidable element 122 urged by a captive spring 123 in a direction to seat against a shoulder 124 in the casing 66. Another bore 125 which may be of smaller diameter than the bore 121 is positioned in the casing 66 in axial alinement with the bore 121 and one end communicatively connected to the compartment 110 and the other end communicatively connected to the sixth annular groove 75 through the passage 126. It will also be noted from FIGURE 4 that the bore 125 is communicatively connected to the secondary inlet port 104. The slidable element 122 of the relief valve 120 is provided with a small passage 127 which communicates the spring chamber 128 with the compartment 110 as a breather. By selecting the size of the passage 127 appropriately the passage 127 will serve as a dampening means for preventing rapid movement of the slidable element 122 thus avoiding chattering.

The general construction of the control valve 65 has now been described except the means .for actuating movement of the movable valve member on plunger 81. It will be noted from FIGURE 4 that the rightward end portion of the control valve 65 is a centering device, indicated generally at 129, for urging the movable valve member 81 toward central or neutral position. The centering device 129 essentially consists of a captive spring 130 disposed between two annular collars 131 and 132. The collar 131 is in slidable relation with respect tothe right end portion 133 of the valve plunger 8 1. 'Ilhe collar 131 is also slidable Withinthe bore 173.4 of the closure member 68 as may be seeninFIGURE4. How.

ever, the land 89 ofthe valve plunger 81 is engageable with the collar 131 for rightward movement in the bore 134. Leftward movement of the collar 131 is limited by the shoulder 135 in the housing 6 6. The collar 1 32 isV disposed at the other end of the spring 130 in slidable relation with reference to t-he portion 133 of the valve plunger 81. Rightward movement. ofthe collar 132 is limited by the shoulder 136 in the closure member 68. On the other hand, a leftward movementof the valve plunger 81 also moves the collar 132 leftwardly by the engagement of the head or snap ring 137 connectedrigidly to the portion 133 of the plunger 81.

As shown in FIGURE 4, the valve plunger 81 is in a neutral position. If the plunger 81 is moved leftwardly the collar 131 remains engaged with the shoulder 135 while the coll-ar 132 is moved'leftwardly in the bore 134 with the plunger 81 by engagement with the head o-r snap ring 137 thereby further compressing the spring 130. On the other hand, if the plunger 81 is moved rightwardly, the land 89 thereof engages the collar 131 for slidable movement in the bore 134 While the collar 132 is in abutting relation with the shoulder 136 thereby further compressing the spring 130. From the foregoing, it can be seen that the centering device 129 urgesl the plunger 81 toward the neutral position. as illustrated in FIGURE 4.

Now in order to actuate movement of the valve plunger 81 from a neutralposition to an operating position, the control valve 65 is provided with a servo-motor. This servo-motor may conveniently be comprised of a one-way acting left cylinder, generally indicated at 138 and a one-way acting right cylinder, generally indicated at 139. The piston 140 of the cylinder 138 may be an integral part of the plunger 81 or. may be a separate element slidable in the bore 141 in the casing 66in abutting relation with the plunger 81 as shown in FIGURE 4. Similarly the piston 142 of the cylinder 139 may be an integral part of the plunger 81 or may he a separate element slidable in the bore 143 in the closure member 6 8. in abutting relation with the plunger 81'. From this it can be seen that if the small chamber 144. is pressurized by tiuid under pressure entering through at least one of the conduits 145, 146 and 147, the piston 140 urges movement of the valve plunger 81 in a rightward direction from a neutral position to an operating position. It should be noted that in order for the valve plunger 81 to move rightwardly, the chamber 144 must necessarily be encrgized with suicient fluid pressure so that the piston 140 overcomes the resisting force exerted by the centering device 129. Likewise, it may also be seen that the small chamber 148 is pressurized by uid under pressure entering through at least one of the conduits 149, 150 and 151 the piston 142 urges movement of the v alye plunger 81 in a leftward direction from aneutral position to an operating position. Again itshould be noted that in order for. the valve plunger 81 to move leftwardly, the chamber 148 must necessarily be energized with sutlicient uid pressure so that the p iston 142 overcomes the resisting force exerted by the centering device 129.

Now in order to prevent the occurrence of uid pressure in 4the left opening 152 of the bore 69 from inhibiting the movement of the plunger 81, a breather passage 153 is provided in the housing 66 communicatively connecting the opening 152 with the first annular groove 70 which groove is communicatively connected with thedischarge port 90. Likewise, the spring chamber or bore 1s provided with a breather passage 154 communicatively connecting the bore 134 with thel c0nduit.92 which conduit is communicatively connected the` discharge port 90. Thus there is no uid pressure diierentialbetween the opening 152 andthe bol'v 134 FIGURE illustrates in schematic form an hydraulic system suitable for employment with this invention. It will be seen that there are two basic fluid circuits shown, one being the control circuit andthe other the working circuit. For convenience the control circuit will be described first.

The numeral 155 is a manually operable steering wheel. The wheel 155 through steering shaft 156 drives rotatably a small positive displacement pump indicated at 157. Rotation of the wheel 155 in one direction causes movement of liuid from the conduit 146 to the conduit 150. Conversely, rotation of the Wheel 155 in the other direction causes movement of fluid from the conduit 150 to the conduit 146. A pair of oppositely connected small relief valves 153 and 159 may conveniently be provided so that by-pass condition occurs in the event that fluid pressure in either of the conduits 146 or 150 exceeds apredetermined value.

The conduits 146 and 150 are communicatively connectedto the servo-motor 138, 139 as shown in FIG- URE 5. The conduits 147 and 151 communicatively connected to the cylinders 138 and 139, respectively, terminate at the outlet sides of a pair of small check valves 160 and 161, respectively, as shown in FIGURE 5. The inlet sides ofthe check valves 160Aand 161 are connected to the discharge port through the conduit 92. Normally there is no movement of fluid through the conduits 147 andv 15,1 or the check valves 160 and 161. The sole purpose of the check valves 160-and 161 is to permit replenishment of uid in the control circuit in the event that tiuid'in the control circuit is lost by leakage or otherwise.

'I'he conduit 145v communicatively connects the small chamber 144 of the left servo-motor cylinder 138- with the port- 64 and chamber 63 of the right servo-pump cylinder 54. Similarly, the conduit 149 communicatively connects the small chamber 148 of the right servo-motor cylinder139 with the port 60 and chamber 59 of the left servo-pump cylinder 53.

From the above it can be seen that the control circuit includes the displacement pump 157, the left servo-motor cylinder 1-38 and right servo-motor cylinder 139, the left servo-pump cylinder 53 and right servo-pump cylinder 54, small relief valves 158 and 159 interconnected cornmunicatively through conduits 146, 150, 147, 151, 145 and 149^as shown in FIGURE 5.

The working circuit of the hydraulic system will now be described.

The casing 16 of the reversible motor 29 (FIGURE 2) may for convenience be entirely closed so that it can serve as a reservoir 162 (FIGURE 5) for the primary source of fluid under pressure 105 and the secondary source of uid under pressure 108. Thus the fluid reservoir is designated by the numeral 162 which may be suitably vented ast schematically indicated at 163. The reservoir 162 is communicatively connected through filter 168 to the inlet sides of' the sources of fluid pressure 105 and 108 by the conduitA 164. The outlet side of the primary source of lluidpressure 105 is communicatively connected to the primary inlet port 103 of the controlv valve 6 5 through the conduit 106. It will be noted that reverse ilow of lluid through conduit 106 is prevented by the unidirectional flow valve 107 interposed' therein. The outlet sideA ofthe secondary source of tluid pressure 108. is communicatively'connected to the secondary inlet port 104 ofthe control valve 65 through the conduit 109. The conduit 94 communicatively connects the second annular groove 71. through the irst outlet port^93 ofthe control valve 65 with the chamber 3,6 of the rstram 30; Similarly, the conduit 96 communicatively connects the fourth Yannular groove 73 through the second outlet port of the controlvalve 65 with the chamber 44 of the second ram 31. The conduit 92 communicatively connects the fifth annular groove 74 through the port 91 and' conduit 101 with the discharge port 90. Also the conduit communicatively connects the inlet sides of the small check valves 160 and 161 with the discharge port 90 through the conduit 101. The outlet side 100 of the check valve 97 is communicatively connected to the sump or reservoir 162 through the conduit 165. The conduit 169 is merely a bleeder line communicatively connected to the conduit 161 for conveniently lubricating thebearing members of the pivotal connection and forms no part of this invention.

Operation The fluid power steering system embodying this inventlon as illustrated in the drawings is in condition for a .straight course of travel of the tractor 1i) and its associated trailer 13. Thus, the control valve is in neutral position as shown in FIGURES 4 and 5 and the pistons 32 and 46* of the rams 30 and 31, respectively, are in medial position as illustrated in FIGURES 2 and 5.

Referring to FlGURE 5, the control circuit above described is in static condition, that is to say, there is no movement of uid therein. It will be noted that the control circuit is a closed iluid circuit independent of the primary fluid pressure source 105 and secondary fluid pressure source 168. It will also be noted that the cams 57, 57' (FIGURE 5) and the modified form of cam 57 (FIGURES 6 and 7) maintain pistons 55 and 61 in medial position indicating that the course of travel of the tractor 16 and trailer 13 is in a straight line. The ilow of uid through the working circuit when the control valve 65 is in neutral position will now be described.

With continued reference to FIGURE 5, iiuid under pressure from the primary pump 10S flows through the unidirectional valve 107 to the primary inlet port 163 of the control valve 65 through conduit 106. From the port 163 the fluid passes into the third annular groove 72 through the elongated compartment 110. Since the movable valve member 81 is in neutral position, none of the lands S6, 87, 38 and 89 register with lands '76, 77, 78, 79 and Sil so fluid entering the third annular groove 72 may communicate with the first annular groove 70, second annular groove 71, fourth annular groove 73, fifth annular groove 74 and sixth annular 'groove 75. However, the only outlet for fluid is by way of the iirst annular groove 76 in communication with the discharge port 90 through port 91 and conduits 92 and 101. The discharge port 90 may also be considered the inlet side of check valve 97. The check valve 97 is adjusted to open at a low Value, for example p.s.i., so that fluid by-passes therethrough to the sump or reservoir 162 through the conduit 165. Thus when the control valve 65 is in neutral position as shown in FXGURES 4 and 5, the fluid pressure within the bore 69 is maintained at a value set by the check valve 97. From this it can be seen thatboth the lirst ram and second ram 31 are energized equally at low pressure from the uid in the second annular groove 71 communicatively connected to the lirst ram 30 through the conduit 94 and the fourth annular groove 73- communicatively connected to the second ram 31 through the conduit 96. Since both rams 30 and 31 are energized equally the pistons 32 and 40 of the rams 30 and 31, respectively, being opposed to each other will not move. The force exerted by the pistons 32 and 40 maintains the teeth 35 of the rack member 34 and teeth 43 of the rack member 42 in constant force of low magnitude with the teeth of the pinion gear 25 thus eliminating backlash and thereby reducing wear on the teeth. This anti-backlash feature provides noiseless operation and eliminates dam age to the teeth through pounding during operation of the steering mechanism. It Will be noted that this antibacklash feature is present during all operational move ments of the steering mechanism as will be evident in the further discussion. It should now be clear that when the control valve 65 is in neutral position, iiuid from the ypump 165 is eiectively bypassed back 'to the reservoir The iuid from the secondary source of uid under pressure 108 enters the control valve 65 at the secondary inlet port 104 through the conduit 109. From the port 104 thekiluid passes .into the sixth annular groove 75 through the bore 125 and passage 126. Since the` movable valve member 31 of the control valve member 65 is in neutral position, the fluid under pressure from the secondary source 103 merges with the iiuid from the primary source and is by-passed back to the reservoir 162 in the same manner as that described for the primary source 105. 1t will be noted that the relief valves 114 and remain in closed or seated position.

Now suppose the operator rotates the steering wheel 155 in one direction as in a normal steering movement. The displacement pump 157 causes a pressure rise in the conduit 146 of the control circuit above that in the conduit 150. Since, at least for the moment, the fluid in the conduits 145, 147, 149 and 151 is static, there is a pressure differential created whereby the pressure in the small chamber 144 of the left cylinder 138 is greater than the pressure in the small chamber 148 of the right cylinder 139. When the aforementioned pressure difierential is great enough to overcome the action of the centering device 129, the piston moves the plunger 81 of the control valve 65 rightwardly to a first forward position. When the first forward position of the plunger 81 is reached the land 86 has moved sutiiciently to register with land 77 thereby terminating fluid communication from the third annular groove 72 to the second annular groove 71. Simultaneously the land 87 has moved sutliciently to register with land 79 thereby terminating ilow of fluid between the fourth annular `groove 73 and the fifth annular groove 74. Meanwhile the land 88 has not moved sufliciently to register with land Sil thereby permitting the fluid from the secondary source of fluid under pressure 16S to continue to be by-passed in the same manner as that for neutral position as previously explained.

With the plunger 81 in the first forward position only `the uid under pressure from the primary pump 105 is utilized for steering. The fluid yfrom the pump 105 enters the primary inlet port 163 of the control valve 65 and passes into the third annular groove 72 through the compartment 114i. From the third annular groove 72 the fluid passes into the fourth annular groove 73 and into the chamber i441 through the conduit 96 thus energizing the second ram 31 `at high pressure. The ram 31, therefore, expands to move the pinion gear 25 relatively clockwise as viewed in FGURE 5. Meanwhile the first ram 36 is caused to retract by movement of the pinion 25, rack member 3d and piston 32. The fluid in the chamber 36 o-f the ram 30 exhausts into the second annular gro-ove 71 through the conduit 94. From the second annular lgroove 71 the uid passes into the irst annular groove 7i? which groove is in communication with the discharge port 9d. v From the discharge port 9i) the iluid passes through `the checkvalve 97, in the manner described previously, to the reservoir 162 through the conduit 165.

In the event that the operator continues a normal steering movement in the same direction until a maximum angular displacement between the tractor 10 and trailer 13 is reached, piston 4) of the ram 31 will have reached its maximum expansible limit. When this condition is reached, no further flow of liuid is possible in the conduit 96. Thus, a further pressure increase may immediately occur in the third annular groove 72 in compartment 11G. Under such conditions when the pressure reaches a predetermined limit, the relief Valve 114 opens to relieve the excess 4iluid under pressure in the compartment 116 to bleed into the bore 112 through the passage 113V g to the fifth annular groove 74 where it merges with thefiuid from the secondary source of uid under pressure 10S and is by-passed back to the reservoir 162 through the port 91, conduits 92 and 101, discharge port 9), check valve 97 and conduit 165. Tlius,-damage of the apparatus by excessive pressure is avoided.

Now further suppose that theoperator nds that-the 1.1 normal steering movement response is insuflcient to meet his needs at a given particular time owing to the limited delivery capacity of the pump 165. He then applies a greater effort in rotating the steering wheei 155 which through the resulting action o-f the displacement pump 157 creates a greater increase in pressure in the conduit 1li-6 over that in the conduit 150. rThis movement causes aV greater pressure in the control circuit which further increases the pressure in the small chamber 144 of the left cylinder 138. Thus, kthe piston 140 drives the plunger $1 of the control valve 65 rightwardly beyond the first forward position above described to a second forward position now to be described, At this point it should be noted that when the plunger 81 is moved rightwardly to the second forward position fluid under pressure from both sources 10S and 168 are combinedly employed in effecting steering movement of tbe tractor 10 and trailer 13.

When the plunger 81 is movedto its extreme rightward limit (second forward position) the land 86 is in registration with the land 77 thereby preventing fluid communication from the third annular groove 72 to the second annular groove 71. The land 87 also is in registration with the land 79 thereby preventing ow of fiuid between the fourth annular groove 73 and fifth annular groove 74. However, when the plunger 81 is moved to its extreme rightward position (second forward position), the land S3 registers with the land Si) thus terminating flow of fluid from the` sixth annular groove 75 to the fifth annular groove 74. From this it can be seen that since fluid flow in the passage 126 and sixth annular groove 75 is terminated, fluid pressure in the bore 125 Will immediately rise which pressure rise unseats the second relief valve 120 thereby merging flow of fluid from the secondary pump 1984 with the fluid from the primary pump 165 in the compartment 110. ri`hus, oid under pressure from both sources passes into the third annular groove 72, thence to the ram 31, through the conduit 96. As in the case of the first forward position of the plunger Si, the expanding ram 31 causes retraction of the ram 3ft and the exhausting of fiuid from the chamber 36 is the same as that described for the first forward position.

Assuming again that the tractor 1f) and trailer 13 are alined for a straight course of travel and the operator wishes to effect a normal steering turn in the other direction. He rotates the steering wheel 155 in the other direction in a normal steering movement. The displacement pump 157 now operates reversely from that previously described and causes a pressure rise in the conduit 15.0 of the control circuit above that in the conduit 146. Since, as before, the fluid in the conduits 145, 147, 149 and 151, is static, there is a pressure differential created whereby the pressure in the small chamber 148 of the right cylinder 139 is greater than `the pressure in the small chamber 144 of the left cylinder 138. Again, as before, when the pressure differential is great enough to overcome the action of the centering device 129, the piston 142 moves the plunger 81 of the control valve 65 leftwardly from` neutral position to a first reverse position. When the first reverse position is` reached, the land 86 has moved sufficiently to register with land 76 thereby terminating fluid communication from the second annular groove 71 to the first annular groove 70. Simultaneously, the land 87 has moved sufficiently to register with the land 78 thereby terminating flow of uid between the fourth annular groove 73. and the third annular groove 72, Meanwhile the land 89 has not moved sufficiently to register with the land 80 thereby permitting the uid from the secondary source of fluidV under pressure 1.08 t continue to be bypassed inthe same manner as that for neutral position aspreviousiy explained. With the plunger 81 in the first reverse position only the fiuid under pressure from the primary pump 105 is utilized for steering. The fluid from the pump 165 enters the primary inlet port 103 of the control valve 65 and passes into the third an- Ain: nular groove 72 through the compartment 11i?. From the third annular groove 72 the fluid passes into the second annular groove 71 and into the chamber 36 through the conduit 94- thus energizing the first ram 3f! at high pressure. The ram 3G therefore expands to move the pinion gear 25 relatively countercloclrwise. Meanwhile, the second ram 31 is caused to retract by movement of the pinion 25, rack member i2 and piston 40. The fluid in the. chamber 44 of the ram 31 exhausts into the fourth annular groove 73 through the conduit 96. From the fourth annular groove 73 the fluid passes into the fifth annular groove 74 which groove is in communication with the discharge port 9) through port 91 and conduits 92 and itil. From the discharge port 9G the fiuid passes through the check valve 97 in the manner described previousfy to the reservoir 162 through the conduit 165.

Now again supposing that the operator finds that the normal steering movement response is insufficient to meet his needs at a given particular time owing to the limited delivery capacity of the pump 165. He thon applies a greater effort in rotating the steering wheel in the same direction which through the resulting action of thc displacement pump 157 creates a greater increase in pressure in the conduit 154i over that in the conduit 146. This movement causes a greater pressure in the control circuit which further increases the pressure in the small chamber 143 of the right cylinder 139. Thus, the piston 142 drives the plunger 31 of the control valve 65 loftwardly beyond the first reverse position above described to a second reverse position now to be described. It should be noted that when the plunger 81 is moved leftwardly to the second reverse position, fluid under pressure from both sources 1435 and fitti are combinedly employed in effecting steering movement of thc tractor 10 and trailer i3.

When the plunger 31 s moved to its extreme leftward limit (second reverse position), the land 86 is in registration with the land 76 thereby preventing fluid communication from the second annular groove 71 to the first annular groove 76. The land S7 also is in registration with the land 78 thereby preventing flow of fluid between the fourth annular groove 73 and the third annular groove 72. However, when the plunger S1 is moved to its extreme leftward position (second reverse position), the land 3E* registers with the land {if} thus terminating ow of fluid from the sixth annular groove i5 to the fifth annular groove 74. From this it can be seen that since fluid flow in the passage 125 and the sixth annular groove 75 is terminated, fluid pressure in the bore 125 will immediately rise which pressure rise unseats the second relief valve 12) thereby merging flow of fluid from the secondary pump 1-38 with the fluid from the primary pump in the compartment 11i). Thus, fluid under pressure from both sources passes into the third annular groove '72, thence to the ram 3f) through the conduit 94 and second annular groove 71. As in the case of the first reverse, position of the plunger 81, the expanding ram 3f) causes retraction of the ram 31 and the exhausting of fluid from the chamber 44 is the same as'that described for the first reverse position.

Up to this point, means have been described whereby the operator, by manipulating manually the steering wheel 15,5 appropriately, may shift the plunger 81 of the controlvalve into any one of five positions, namely, neutral position, first and second forward positions, and first and secondreverse positions. In order that the operator may have the ybenefit of road feel in the steering operation, a means forfolloW-up for progressive steering in this invention will now be described.

The follow-up means employed in the control circuit is essentially of the telemeter type system whereby means are provided for progressively equalizing the fluid pressure in the left cylinder 138 with that of the right cylinder 139 of the servo-motor so that as the tractor 1G reaches a predetermined angular displacement with respect to the trailer 13, the plunger 81 of the controlrvalve 65 is progressively moved to neutral position independently of the steering wheel 155 and associated displacement pump 157. l

Suppose, for example, the operator desires to alter the course of travel from a straight line to an arcuate path in one direction in an ordinary normal steering movement. In order to accomplish an arcuate path of travel it is necessary that the tractor 10 be angularly displaced with respect to the trailer 13. The operator rotates the steering wheel 155 to a predetermined position and manually maintains the wheel 155 tixedly` in the assumed position. As previouslydescribed, this normal steering movement creates a pressure differential in the control circuit whereby the left cylinder 138 of the servo-motor actuates the plunger 81 in a rightward direction from neutral position to the first forward position (or to the second forward position depending upon the extent and rate of rotation the operator imparts to the steering wheel 155). Immediately the ram 31 is energized and commences to expand while the ram 30 concurrently commences to retract further from the position illustrated in FIGURE 5. Simultaneously, the pinion gear 2S begins to rotate clockwise which movement imparts an angular displacement between the tractor 10 and trailer 13. At the same time the cam surface 53 of the cam 57 on the second rack member 42 begins to move leftwardly as viewed in FIG- URE 5. The cam surface 58 thus causes retractive movement of the servo-pump 53 through the actuating pin 56 thereof which pin 56 is a follower element in respect to the cam 57. Thus, the piston 55 of the servo-motor 53 forces fluid in the chamber 59 thereof into the conduit 149 which communicates with the small chamber 14S of the servo-motor cylinder 139 thereby gradually elevating the fluid pressure in the small chamber 14S. Simultaneously, the servo-pump 54 is permitted to expand from the position shown in FIGURE 5 by the faction of the actuating pin or Ifollower element 62 o-n the cam surface S' of the cam 57 on the retracting rack member 34. Thus the chamber 63 increases in volume admitting additional fiuid therein from the small chamber 144 of the` servo-motor cylinder 138 communicatively connected to` the conduit 145. The decrease inuid pressure in the small chamber 144 with a corresponding increase of ffuid pressure in the small chamber 148 is thus progressive in character as the pinion gear 2S rotates until the pressure in the two chambers 144 and 14S approach equal value. As the pressure differential in the two chambers 144 and 143 decreases the valve plunger 81 of the control valve 65. progressively moves toward neutral position assisted by the centering device '129.' When the plunger 81 reaches neutral, by-pass of fiuid from the pumps 105 and 163 is again reestablished `and the ram 31 is no longer energized which halts any further rotation of the pinion 25. Thus the tractor 16 has assumed an angular displacement with respect to the trailer 13 and will remain at such angular displacement until the operator again r0- tates the steering wheel 155. Obviously, steering in the other direction will produce corresponding results in the opposite direction.

It will be noted from FIGURE 5 that the piston 55 of the servo-pump 53 and the piston 61 of the servo-pump 54 move in parallel relation. Thus it is apparent that the volumetric displacements of the servo-pumps 53 and 54 should be equal to each other and, further, the displacement of each pump 53 and 54 must be appropriately selected with reference to the displacement pump 157 and servo-motors 13S and 139 so that incremental rotation of the steering wheel 155 will produce a corresponding angular displacement of the tractor 10 with respect to its trailer 13.

Reference is now made to FIGURE 7 illustrating a modified form of the invention for actuating the follow-up means. Assuming for the moment that the operator actuates the steering wheel 155 as just previously descri-bed, it will Ibe seen that the servo-pumps 53 and 54 function in exactly the same manner as before. However, the cam means for actuating the servo-pumps 53 and 54 is modified over that shown in FIGURES 2 and 5. When the ram 31 is energized, as before, and commences to expand while the ram 3f) concurrently commences to retract further'from the position illustrated in FIGURE 7, the pinion gear 25 rotates clockwise which move-ment imparts an angular displacement between thettractor 10 and the trailer 13. At the same time the cam surface 53" of the cam 5'7" mounted on the pinion gear 25 rotates clockwise respective to the servo-pump 53 and servo- 'pump 54. The servo-pump 53 is ycaused to further retract by the action of the cam surface 58" on the actuating pin 56. Thus, the piston '55 forces uid in the charnber 59 into the conduit 149 which communicates with the small chamber 148 of the cylinder 139 therebyr gradually elevating fluid pressure in the small chamber 14S. Simultaneously, the servo-motor 54 is permitted to expand from the position shown in FIGURE 7 by the action of the actuating pin 62 on the cam surfaceSS" of the rotating cam 57". Thus, the chamber 63 increases in volume admitting additional fluid therein from the small chamber 144 of the cylinder 138 communicatively connected through the conduit 145. The decrease in fiuid pressure in the small chamber 144 with a corresponding increase in iiuid pressure in the small chamber 14S is thus progressive in character as the pinion gear y25 rotates until the pressure in the two chambers 144 and 148 approach equal value. As the pressure differential in the two chambers 144 and 143 decreases the valve plunger S1 of the control valve 65, as before, progressively moves toward neutral position assisted by the centering device 129. When the plunger 81 again reaches neutral, by-pass of fluid from the pumps 105 and 168 is again reestablished and the ram 31 is no longer energized which halts any further rotation of the pinion gear 25. Thus, the tractor 10 has assumed an angular displacement with respect to the trailer 13 and will, as before, remain at such angular displacement until the operator again rotates the steering wheel 155. Obviously, steering in the other direction will produce corresponding results accordingly.

It should be noted that particularly when the tractor 16 and its trailer 13 are traveling over rough or uneven terrain, any force imparted to one with reference to the other, which force tends to alter the angular displacement ,between the two, is immediately transmitted to the servo-pumps 53 and '54 which will move the plunger S1 from the neutral position to an operating position to counteract such force inthe direction necessary to correct the alternation in angular displacement. This is true for either type of camming means shown in FIGURES 2 and 5, or, FIGURES 6 and 7. Such force also affects uid pressure in the conduits 146 and 150 which acting through the displacement pump 157 reflects back to the operator at the steering wheel 155. Thus, the operator has the benefit of road feel similar as that in steering an automobile for example, when either form of the camming means just described is employed.

It will be noted that in FIGURE 6 the servo-pumps 53 and 54 are disposed at right angles with reference to that indicated in FIGURE 7. It will be observed that the cam means illustrated in FIGURES 6 and 7 that while the servo-pumps 53 and 54 may be positioned radially about the king pin 22 it is apparent that the actuating pins 56 and 62 of the servo-motors must be radial, while in the case of the first form of the invention illustrated in FIG- URES 2 and 5 the servo-pumps 53 and '54 may be positioned with much more latitude. Furthermore, it is not necessary in the form of the invention illustrated in FIG- URES 2 and 5 that the actuating pins 56 and 62 be in radial alinement with the king pin 22.

Having thus described embodiments of the invention, it can now be seen that the objects of the invention have been fully achieved and it must be understood that changes and modifications may be made which do not depart from the spirit of the invention nor uponthe scope thereof as defined in the appended claims.

What is claimed is:

1. For a vehicle `of the kind described having a twowheel tractor unit pivotally connected to a trailer unit, said vehicle having a uid power steering system capable of angularly displacing one of said units with respect to the other of said units, said steering system consisting of a rack member supported on one of said units and a pinion gear connected to the other of said units in steering engaging relation, a reversible fluid motor operatively connected to said rack member and a source of fluid power therefor, a uid working circuit consisting of a servomotor operated control valve and a tiuid servo-motor therefor interposed operatively between said source and said motor for controlling the angular displacement between said units, and a fluid control circuit having a manually operated fluid displacement pump for energizing said servo-motor; a follow-up means for moving said control valve from an operating position to a neutral position when a predetermined angular displacement between said units is reached comprising a cam disposed on said rack member, a servo-pump mounted on said vehicle positioned in operative relation with said cam, said servopump being communicatively connected to said uid control circuit whereby said servo-pump actuates said servomotor responsive to movement of said rack member in a direction for moving said control valve from an operating position to a neutral position when said predetermined angular displacement between said units is attained.

2. For a vehicle of the kind described having a ytwowheel tractor unit pivotally connected to a trailer unit, said vehicle having a fluid power steering system capable of angularly displacing one of said units with respect to the other of said units, said steering system consisting of a rst rack member and a second rack member disposed in opposed relation on one of said units and a pinion gear connected to the other of said units meshed in steeringengaging relation, a first ram connected to said first rack member and a second ram connected to said second rack member in operative relation, a source of fluid under pressure, a tiuid working circuit consisting of a servomotor operated control valve and a uid servo-motor therefor interposed operatively between said source and said rams for controlling the angular displacement between said units, and a fluid control circuit having a manually operated luid displacement pump for energizing said servo-motor; a follow-up means for moving said control valve from an operating position to aneutral position when a predetermined angular displacement between said units is reached comprising cam means disposed on at least one of said rack members, a servo-pump mounted on said vehicle positioned in operative relation with said cam means, said servo-pump being communicatively connected to said liuid control circuit whereby said servopump actuates said servo-motor responsive to movement of said cam means in a direction for moving said control valve from an operating position to a neutral position when said predetermined angular displacement between said units is attained.

3. For a vehicle of the kind described having a twowheel tractor pivotally connected to a trailer, said vehicle having a fluid power steering system capable of angularly displacing said tractor with respect to said trailer, said steering system consisting of a iirst rack member and a second rack member disposed in opposed relation on said tractor and a pinion gear connected to said trailer meshed in steering engaging relation, a first ram connected to said iirst rack member and a second ram connected to said second rack member in operative relation, a source of uid pressure on said tractor, a fluid working circuit consisting of a servo-motor operated control valve and a fluid servo-motor therefor interposed operatively between said source and said rams for controlling the angular displacement between said tractor and said trailer, and a iiuid control circuit having a manually operated uid displacement pump for energizing said servo-motor; a followup means for moving said control valve from an operating position to a neutral position when a predetermined angular displacement between said tractor andsaid trailer is reached comprising a trst cam disposed on said first rack member and a second cam disposed on said second rack member, a servo-pump having a rst cylinder and a second cylinder mounted in opposed relation on said tractor, said irst cylinder being positioned in operative relation with said first cam and said second cylinder being positioned in operative relation with said second cam, said cylinders being communicatively connected to said fluid control circuit whereby said cylinders responsive to movement of said cams actuate said servo-motor of said control valve in a direction for moving said control valve from an operating position to a neutral position when said predetermined angular displacement between said tractor and said trailer is attained.

References Cited in the tile of this patent UNITED STATES PATENTS 2,532,786 Richter Dec. 5, 1950 2,614,644 Gustafson Oct. 21, 1952 2,680,491 Davidson June 8, 1954 2,917,125 Donner et al Dec. 15, 1959 

